1. Field of the Invention
The present invention relates to an optical recording apparatus adapted for use in recording information on a write-once type compact disc (CD) where additional recording is possible merely once.
2. Description of the Prior Art
In a CD, a subcode is recorded in addition to audio data in such a manner as to be included in a predetermined amount of record data to constitute one unitary frame of information.
FIG. 4 shows a format of record signals constituting a unitary information frame of a subcode. In recording information on a CD, there are sequentially recorded EFM frames each composed of a total of 588 bits which comprise, in the direction of a time series, a 24-bit frame sync signal (FS), and 8-bit subcode, data of 6 samples.times.2 channels, and a data portion consisting of parity bits thereof (DATA).
As shown in FIG. 4, 1 frame is composed of 98 EFM frames. And in the data of each frame, there are included 8 subcodes ranging from P to W. One bit of each of such subcodes P to W is contained in 1 EFM frame, and 1 information unit is constituted of 1 frame (98 EFM frames=98 of each subcode bits).
Out of such 8 subcodes, the subcode Q serves as address information consisting of a track number (e.g. program number) and time information. FIG. 5A shows the content of 1 frame corresponding to 1 information unit of the subcode Q, in which the first 2 bits S0, S1 are used as a subcode sync pattern; the next 4 bits are used as control bits CONTROL indicating the presence or absence of preemphasis and the type thereof; the next 4 bits as an address ADR; the next 8 bits as a track number TNO; next 8 bits as index information INDEX; the next 24 bits represent the elapse time of the relevant program (8-bit minute value MIN, 8-bit second value SEC, and 8-bit frame number value FRAME); the next 8 bits are composed entirely of bits-0 and are not used; the next 24 bits represent the absolute elapse time from the beginning of the disc (8-bit minute value AMIN, 8-bit second value ASEC, and 8 -bit frame number value AFRAME); and the last 16 bits are used as an error detecting CRC code generated for the 1-frame of subcode except the sync pattern.
In a write-once type CD also, the signal recording format is exactly the same as that of the ordinary CD mentioned above. However, in the write-once type CD where additional recording is performed, there arises a problem with regard to the joint between the preceding record portion and the present record portion. In the standard (orange book) for the write-once type CD, it is prescribed that, when the recording has been stopped, the last frame of the record data is to include 26.+-.1 EFM frames (FIG. 5C) from the first subcode sync pattern (FIG. 5B) of 1 frame.
In the recording apparatus designed for such write-once type CD, a technique may be so contrived that, when the recording operation is stopped and then resumed as shown in FIG. 5C, the data after 26.+-.1 EFM frames from the subcode sync pattern in the first frame of the new portion is recorded in succession to the preceding record portion so that both data can be joined together seamlessly.
In this case, the practical data at the joint are such as those shown in FIG. 5D. Namely, the subcode Q of the preceding last frame denotes a track number [5], [02] minutes, [12] seconds, [34] frames, and an absolute time of [15] minutes, [43] seconds, [21] frames; whereas the data recorded in actual practice is the index data [0 1 05 03] except the information denoting the track number and the absolute time represented by solid lines in FIG. 5D.
Meanwhile the subcode Q of the first frame of the data to be recorded in succession to the aforementioned preceding record portion denotes an increased track number [06], [00] minute, [00] second, [00] frame, and an absolute time of [15] minutes, [43] seconds, [21] frames. However, the data recorded in actual practice include the time data represented by solid lines in FIG. 5D and an error detecting code CRC-2 relative to the subcode Q of the first frame of the data to be recorded additionally.
Therefore the subcode Q of the frame at the joint is rendered indefinite. Since the error detecting code CRC-2 recorded as the subcode Q of one frame at the joint is generated with regard to the subcode Q of the first frame of the data to be additionally recorded, it follows that the subcode Q of the first frame is detected as an error by the error detecting code CRC-2. However, as the CRC code is effective merely for error detection and not for error correction, the subcode Q of the frame at the joint is discarded without being used.
Consequently the apparatus is kept free from a malfunction due to the above, but it becomes impossible to properly obtain the address information which is the subcode Q of the first frame at the restart of the recording operation. Besides, there may occur another disadvantage that accurate reading of the subcode is rendered impossible because of some dust or flaw. And in case the subcode Q fails to be read accurately in the successive frames, exact arrival at the proper position is not achievable when such portion is searched, or a long time may be required for arrival at the desired position.
The problems described above arise with regard to other subcodes as well as the aforementioned subcode Q.